Heterogeneous oxygen distribution in tumor microenvironment can contribute to therapy failure. Anoxia and severe hypoxia in microregions of solid tumors due to increased distances between blood vessels results in decreased activity of cells or up-regulation of hypoxia linked cellular mechanisms, such as increased expression of glycolytic enzymes, glucose transporters, pH homeostasis enzymes, and angiogenic growth factors. All of these adaptations are in favor of survival and proliferation of hypoxic cells in adverse conditions making them resistant to therapy.
Methodologies for oxygen measurement in three-dimensional tissues developed so far, based on both optical and electrochemical principles, are restricted to measurements in single time point assuming steady state oxygen distributions. Both time- and depth-resolved continuous mapping of oxygen inside tumor tissue models has not been achieved.